DP83953 datasheet(24/90 Pages) NSC

24 / 90 page

4.0 Functional Description (Continued)

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on its segment, but in addition it is higher in the arbitration

chain. This priority yields no benefits for port A1 since the

ANYXN signal is still active. There are now two sources

driving ANYXN, the MSMs and the collision on port B1.

Eventually the collision on port B1 ends and the ANYXN

extension by the MSMs expires. There is only one collision

on the network (this may be deduced since ANYXN is inac-

tive) so the repeater will move to the

ONE PORT LEFT

state. The RIC2A system treats this state in a similar man-

ner to a receive collision with

PORT M fulfilling the role of

the receiving port. The difference from a true receive colli-

sion is that the switch from packet data to the jam pattern

has already been made (controlled by ANYXN). Thus the

state of COLN has no effect upon repeater operations. In

common with the operation of the

RECEIVE COLLISION

state, the repeater remains in this condition until the colli-

sion and receive activity on

PORT M subside. The packet

repetition operation completes when the

Tw1 recovery time

in the

WAIT state has been performed.

Note: In transmit collision conditions

COLN will only go active if the RIC2A

which contained

PORT N at the start of packet repetition contains PORT M

during the

TRANSMIT COLLISION and ONE PORT LEFT states.

Jabber Protection

A repeater is required to disable transmit activity if the

length of its current transmission reaches the jabber pro-

tect limit. This is defined by the specification's

Tw3 time.

The repeater disables output for a time period defined by

the

Tw4 specification, after this period normal operation

may resume.

Figure 9 shows the effect of a jabber length packet upon a

RIC2A based repeater system. The JABBER PROTECT

state is entered from the

SEND DATA state. While the Tw4

period is observed the Inter-RIC bus displays the IDLE

state. This is misleading since new packet activity or contin-

uous activity (as shown in the diagram) does not result in

packet repetition. This may only occur when the

Tw4 re-

quirement has been satisfied.

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